The present invention relates to an interlayer insulating film, a method for forming the interlayer insulating film and a polymer composition for use in a multilayer interconnect structure of a semiconductor integrated circuit device.
In accordance with the development for increasing the degree of integration of semiconductor integrated circuits, the performance of the semiconductor integrated circuits cannot be smoothly improved because of increase of interconnect delay time derived from increase of capacitance between interconnects, that is, parasitic capacitance between metal interconnects. The interconnect delay time is in proportion to a product of the resistance of metal interconnects and capacitance between the interconnects and corresponds to what is called RC delay.
Accordingly, in order to reduce the interconnect delay time, it is necessary to reduce the resistance of the metal interconnects or reduce the capacitance between the interconnects.
A technique to use copper or copper alloy instead of aluminum-based alloy as an interconnect material for reducing the resistance of the metal interconnects has been reported. Since copper or copper alloy has resistivity as small as approximately ⅔ of that of an aluminum-based alloy material, when a copper material is used as the interconnect material, the interconnect delay time simply calculated is reduced to ⅔ of that attained when an aluminum-based alloy material is used, which results in an operation speed 1.5 times as high as that attained by using the aluminum-based alloy material.
When the degree of integration of semiconductor integrated circuits is further increased, however, even in the case where metal interconnects of a copper material are used, there is a fear that the operation speed may be limited due to the increase of the interconnect delay time. Also, when used as the interconnect material, copper has small resistivity ranking next to silver, but even when metal interconnects of silver are used instead of copper interconnects, the interconnect resistance is reduced merely slightly.
On the other hand, in order to reduce the capacitance between interconnects, it is necessary to lower the dielectric constant of an interlayer insulating film. A conventional interconnect insulating film is made of a silicon oxide film, and the silicon oxide film has a dielectric constant of approximately 4 through 4.5. Therefore, it is difficult to use the silicon oxide film as an interlayer insulating film of a semiconductor integrated circuit with a higher degree of integration.
Accordingly, as an interlayer insulating film having a dielectric constant lower than the silicon oxide film, a fluorine-containing silicon oxide film, a low dielectric constant SOG film, an organic polymer film and a porous film have been proposed.
Among these interlayer insulating films having low dielectric constants, a porous film is regarded as a promising film because it can remarkably lower the dielectric constant. When a porous film is used, the quantity of pores introduced into the film (porosity) is increased so as to realize a low dielectric constant.
When the porosity is increased, however, although the dielectric constant can be lowered, the mechanical characteristic (such as elastic modulus, hardness or an adhesion property) is largely degraded. When the mechanical characteristic is degraded, there is a fear of peeling or destruction of the film caused by a variety of stress occurring during integration process. The various stress herein are, for example, thermal stress caused in metal CMP (chemical mechanical polishing) for forming copper interconnects or annealing performed during the process and stress caused in bonding.
The elastic modulus required of an interlayer insulating film used in a semiconductor integrated circuit is at least 3 GPa or more, and the elastic modulus of a porous film with a dielectric constant of 2 or less is much lower than 3 GPa.
Therefore, in order to solve this problem, a porous silica film with high regularity or a three-dimensional organic polymer film with a diamond structure has been recently proposed.
A porous silica film with high regularity can attain elastic modulus of 10 GPa or more by regularly forming, in the film, honey comb structures each with an opening of several nm.
Also, a three-dimensional organic polymer film with a diamond structure is formed through self-organized polymerization of a two-dimensionally polymerized monomer and a three-dimensionally polymerized monomer each having a diamond structure, and can realize improvement of isotropic mechanical strength. Also, a three-dimensional polymer film with a dielectric constant of 2 or less can attain elastic modulus of approximately 10 GPa.
A porous silica film with high regularity has, however, a problem of high hygroscopicity as well as a problem that a method for forming this film is complicated because it is necessary to make the inner wall of each pore hydrophobic. Furthermore, due to its honey comb structure, the mechanical strength is anisotropic, and its elastic modulus along a direction with small mechanical strength is substantially the same as that of a conventional porous film.
On the other hand, a three-dimensional organic polymer film with a diamond structure has a bonding with high polarity in the molecular structure of the polymer. Specifically, a three-dimensional organic polymer film with a diamond structure has a polyimide structure, a polyimidazole structure or a polyoxazole structure, and such a structure has nitrogen or oxygen designated as a hetero atom. C═O of the polyimide structure, N—H of the polyimidazole structure and —O— of the polyoxazole structure all have high polarizability and an effect to increase the dielectric constant as well as a function to increase the hygroscopicity.
Accordingly, in order to lower the dielectric constant of a three-dimensional organic polymer film with a diamond structure, it is necessary to reduce the density, but when the density is reduced, the mechanical strength is disadvantageously lowered.